Titanium alloys have found extensive application in aircraft, military, medical, and industrial applications. One of the greatest uses of titanium has been in aircraft applications. Aerospace use accounts for over the titanium market. In particular, wrought Ti-6Al-4V alloy is the material most widely specified for use in aircraft applications. See ASM Metals Handbook Grade 5, AMS Spec. 4906, ASTM Spec. 6348.
The primary titanium alloy currently used is the Ti-6Al-4V alloy (over 70%), which was first described in U.S. Pat. No. 2,906,654. The basic manufacturing process used to produce titanium components has been the double consumable arc melting process. This process produces ingots of titanium alloy which must be further processed into billets. They are then formed into a bar or plate, which are typically machined to form a final component. While this and similar manufacturing processes have been used for over 60 years ago, they are generally energy intensive, suffer from high material losses in processing, and are costly. See Titanium in Industry (Van Nostrand 1955), Abkowitz, Burke and Hiltz, and Emergence of the Ti Industry and the Development of the Ti-6Al-4V Alloy (JOM Monograph 1999), S. Abkowitz.
Among potential alternate manufacturing technologies aimed at producing a lower cost titanium product, various powder metal approaches (including the low cost elemental blend powder metallurgy) have been investigated. Niche applications for these “non-melt” processes have been developed. See Titanium Powder Metallurgy: A Review—Part 2, F. H. Froes, Advanced Materials & Processes; October 2012, Vol. 170 Issue 10.
While non-melt processes, i.e., processes that do not involve melting, such as powder metallurgical processes, can produce practical titanium alloys, the resulting mechanical properties of some of the titanium material produced from powdered starting materials could not consistently meet some specific requirements. For example, some non-melt titanium alloys do not meet the minimum tensile and ductility requirements of Ti-6Al-4V wrought product without subsequent thermal mechanical processing, such as, for example, hot working. These lower mechanical properties and other limitations have generally reduced the ability to substitute powder metal Ti-6Al-4V alloys for the traditional wrought Ti-6Al-4V alloys.
Mechanical properties of titanium alloy e also affected by the presence of different elements in the metal material. For example, oxygen has long been recognized as one of the most important and most troublesome constituents in titanium. It is well known that increasing the oxygen content, or content of other interstitial elements such as nitrogen, hydrogen and carbon, decreases the ductility of conventionally processed titanium alloys such as Ti-6Al-4V. Consequently, elevated oxygen content is generally considered severely detrimental to ductility of a wrought titanium product (i.e., produced from ingot melted material).
In addition, oxygen has significant interstitial solubility in titanium. That is, oxygen can dissolve into titanium material and the solute oxygen atoms can take up positions within the titanium alloy lattice structure i.e., interstitially. While interstitial oxygen offers a strengthening effect, it degrades ductility. It is believed that interstitials influence slip planes and dislocations by impeding their movement, thereby increasing strength and decreasing ductility. For at least this reason, the oxygen content of wrought Ti-6Al-4V is limited to 0.20% maximum. And oxygen content above that level is considered too deleterious for commercial use. See “The Effects of Carbon, Oxygen, and Nitrogen on the Mechanical Properties of Titanium and Titanium Alloys,” H. R. Ogden and R. I. Jaffee, TML Report No. 20, Oct. 19, 1955, Titanium Metallurgical Laboratory, Battelle Memorial Institute, Columbus 1, Ohio.
As described below, the present disclosure is directed to an oxygen-enriched titanium alloy formed using powder metals that overcomes at least some of these prior art limitations.